This invention relates generally to an exposure apparatus to be used in a semiconductor lithographic process and also to an anti-vibration system suitable for such exposure apparatus. In another aspect, the invention is concerned with a device manufacturing method to be used with such exposure apparatus.
As regards exposure apparatuses for use in production of semiconductor devices, representative examples are a step-and-repeat type exposure apparatus (called a stepper) in which, while moving a substrate (wafer or glass plate) stepwise, a pattern of an original (reticle or mask) is printed sequentially on plural exposure regions on the substrate through a projection optical system, and a step-and-scan type exposure apparatus (called a scanner) in which, through repetitions of stepwise motion and scan exposure, exposure is repeated to plural exposure regions on a substrate. Particularly, in the step-and-scan type exposure apparatus, through restriction using a slit, only a portion close to the optical axis of a projection optical system is used. Therefore, it enables exposure of a fine pattern with high precision and wide picture angle. In this respect, it is expected as being a major current in near future.
These exposure apparatuses use an anti-vibration system for isolating vibration from the floor on which the apparatus is mounted. In many cases, the anti-vibration system uses an air damper. Generally, an exposure apparatus has a stage system (wafer stage and reticle stage) for moving a wafer or a reticle at a high speed and then for positioning it. Thus, it is required for an anti-vibration system to insulate vibration transmitted from the floor to the exposure apparatus (i.e., isolation of vibration) and also to suppress vibration produced by the stage system itself of the exposure apparatus (i.e., reduction of vibration). In this respect, as regards the air damper, for reduction of vibration, a high natural (vibration) frequency to some extent may be desirable from the viewpoint of response to load change. On the other hand, for isolation of vibration, a natural frequency that is not so high may be desirable. Also, the optimum natural frequency of an air damper may change with load.
Recently, acceleration of a stage movement has become higher and higher for enhancement of processing speed (throughput). In step-and-scan type exposure apparatuses, for example, the stage maximum acceleration reaches 4 G for a reticle stage and 1 G for a wafer stage. Further, the mass and stroke of the stage are becoming larger with enlargement of the reticle or substrate. As a result, the driving force as defined by xe2x80x9cmass of movable memberxe2x80x9d multiplied by xe2x80x9caccelerationxe2x80x9d becomes very large, and the load due to its reaction force is enormously large. Additionally, eccentric load due to stage load shift or variation thereof is also being enlarged.
In conventional air dampers, in order to increase the natural frequency to improve its vibration reduction performance, the diameter of the air damper may be enlarged to increase the pressure bearing area or, alternatively, the capacity of the air reservoir may be enlarged. If, however, the natural frequency is enlarged using this method, a larger space is required for enlargement of the air damper diameter. Also, there is a problem that the natural frequency can not be changed.
It is an object of the present invention to provide an anti-vibration system with an air damper of high natural (vibration) frequency, which is effective to save space.
It is another object of the present invention to provide an anti-vibration system in which the natural frequency of an air damper can be changed.
In accordance with an aspect of the present invention, there is provided an anti-vibration system which comprises a pair of air dampers having driving directions opposed to each other along a vertical direction, and means for controlling inside pressures of said air dampers. The inside pressure controlling means serves to change the air damper inside pressure to thereby change the natural (vibration) frequency of the air damper. The anti-vibration system may be provided with a pair of additional air dampers having driving directions opposed to each other along a horizontal direction.
The present invention is suitably usable in an exposure apparatus, particularly, a step-and-scan type exposure apparatus (scanning exposure apparatus). In that occasion, during acceleration and deceleration of a stage on which a substrate to be exposed is placed, preferably the natural frequency of the air damper may be increased as compared with that during constant speed motion, to thereby improve the vibration reduction performance. For constant speed motion (scan motion) in exposure operation, the natural frequency may preferably be made lower than that in the acceleration/deceleration operation, to thereby improve the vibration isolation performance.
In one preferred form of the present invention, an air damper has a bellows structure so that it can be moved minutely in a direction orthogonal to the driving direction. There may be a linear motor for producing a driving force in a direction parallel to the driving direction of the air damper. Provision of a linear motor enables further improvement in speed of response to displacement correction (vibration reduction) due to eccentric load.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.